This invention relates to drop-on-demand ink jet printing systems and more particularly, to a thermal ink jet printer having an intermediate drum to receive the ink droplets where the droplets are dehydrated prior to transfer to a recording medium, such as paper.
Thermal ink jet printing systems use thermal energy selectively produced by resistors located in capillary filled ink channels near channel terminating nozzles, or orifices, to vaporize momentarily the ink and form bubbles on demand. Each temporary bubble expels an ink droplet and propels it towards a recording medium. The printing system may be incorporated in either a carriage type printer or a pagewidth type printer. The carriage type printer generally has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to a disposable ink supply cartridge and a combined printhead and cartridge assembly is reciprocated to print one swath of information at a time on a stationarily held recording medium, such as paper. After the swath is printed, the paper is stepped a distance equal to the height of the printing swath, so that the next printed swath will be contiguous therewith. The procedure is repeated until the entire page is printed. For an example of a cartridge type printer, refer to U.S. Pat. No. 4,571,599 to Rezanka. In contrast, the pagewidth printer has a stationary printhead having a length equal to or greater than the width of the paper. The paper is continually moved past the pagewidth printhead in a direction normal to the printhead length and at a constant speed during the printing process. Refer to U.S. Pat. No. 4,463,359 to Ayata et al and U.S. Pat No. 4,829,324 to Drake et al for examples of pagewidth printheads.
The major problems associated with producing images directly on plain paper with ink jet technology are the feathering of the image due to ink migration down paper fibers, bleeding of the ink from color to color when producing multi-color images, and a liquid carrier of the ink colorant being absorbed by the paper which produces paper waviness, commonly referred to as cockle.
U.S. Pat. No. 4,538,156 to Durkee et al discloses an ink jet printer wherein an intermediate transfer drum is shown. A transfer drum and printhead are mounted between side plates. The printhead is spaced from the drum, and the printhead nozzles are spaced at equal distances along a line which is parallel to the axis of the drum. The printhead is movable in steps so that on successive rotations of the drum, each nozzle is directed to a new track of a succession of tracks. After all tracks of the transfer drum have been served by a nozzle, a printing medium, such as paper, is brought into rolling contact with the drum to transfer the information on the drum to the printing medium while the printhead is returned to a starting position. The drum is then wiped clean in preparation for receiving the next page of information.
U.S. Pat. No. 4,293,866 to Takita et al discloses a recording apparatus wherein a liquid drop generator is shown which generates ink spots which are formed on an intermediate drum and then transferred onto a paper. The intermediate drum shows an apparatus for color ink jet printing. The intermediate drum has a surface containing the dye or pigment and the ink droplets impact the drum surface, wetting the dye or pigment carrying layer, making it transferable to a recording sheet, together with the liquid whereby a visible printing image may be transferred onto the recording sheet when placed in contact with the intermediate drum by an impression cylinder.
U.S. Pat. No. 4,673,303 to Sansone et al discloses a postage meter utilizing an offset printing roll. A dye plate carried by the roll has a first region for receiving fixed information and a second region for receiving variable information from an ink jet printer. At the beginning of a revolution of the printing roll, the second region is depressed and an inking roll applies ink to the first region. Then the second region is moved into the plane of the first region and an ink jet printing device ejects and propels ink droplets onto the second region to form the variable information thereon. A quality of the printed form of the variable information is sensed. If acceptable, a document is printed. If unacceptable, the first and second regions are both wiped clean and the entire operation is repeated.
The above patents solve some problems associated with ink jet printing which produce images on plain papers, but the major problems of image feathering, color to color bleeding, and paper cockle has not been solved.